A vitreous silica crucible used for pulling up single crystal silicon is mainly manufactured by an arc melting method. In this method, for example, quartz powder is deposited on an inner surface of a mold made of carbon with a predetermined thickness so as to form a quartz powder molded body of quartz deposition, a carbon electrode is mounted above the quartz powder molded body, and the quartz deposition is heated and vitrified by arc discharge, thereby manufacturing the vitreous silica crucible.
Japanese Patent No. 03647688 discloses a technology of manufacturing a vitreous silica crucible by arc melting, and Japanese Patent Application Laid Open Nos. 2002-68841 and 2001-097775 disclose a technology related to an electrode for arc discharge. In addition, Japanese Patent Application Laid Open No. 2003-335532 discloses a technology related to a distance between the electrodes for arc discharge.
Recently, the diameter of a manufactured silicon wafer is increased to exceed 300 mm by a request for efficiency of manufacturing a semiconductor device. Accordingly, a vitreous silica crucible which can pull up single crystal silicon having a large diameter has been required. In addition, improvement of crucible characteristics such as an inner surface state of the vitreous silica crucible, which directly influences on the characteristics of the single crystal silicon, has strongly been required by a request for miniaturization of a semiconductor device.
However, when a vitreous silica crucible having a large diameter of 30 inches to 40 inches is manufactured, the amount of power necessary for melting quartz powder is increased and thus vibration of an electrode, which generates at the time of start-up of arc discharge, is not negligible. When the electrode vibration generates at the time of start-up of arc discharge, current flowing through arc is changed, and the electrode is further vibrated by this current change, thereby further increasing the amplitude of the electrode vibration. As a result, the generated arc becomes unstable and influence on the state of the melted quartz powder is not negligible. In addition, if the electrode vibration is increased, minute pieces stripped from the electrode by the vibration are dropped and thus the characteristics of the vitreous silica crucible deteriorate. In addition, if the amplitude of the electrode vibration is increased, the electrode may be damaged.
In order to prevent the vibration of the electrode, the strength of the electrode should be increased by, for example, being made of a high-strength material or enlarging the diameter of the electrode. With respect to an arc discharge electrode used for manufacturing the vitreous silica crucible, however, this electrode is exhausted and the composition thereof is emitted to a quartz powder melting ambience, resulting in having influence on the characteristics of the crucible. Therefore, only the carbon electrode is used as an arc discharge electrode for manufacturing the vitreous silica crucible. In a case of enlarging the diameter of the electrode, power density deteriorates and, as a result, an arc output deteriorates. In this case, therefore, a processing temperature is decreased and a processed state becomes unstable, thereby having adverse influence on the characteristics of the crucible. In addition, generated fume (silica vapor) is attached to an upper portion of the electrode due to the decrease in the processing temperature, and the characteristics of the vitreous silica crucible can be deteriorated by the dropping of the attached fume. Thus, these means cannot be employed so as to prevent the vibration of the electrode. In addition, the influence of the electrode vibration is caused by the increase in the arc output accompanied by enlargement in the diameter of the crucible.